Staged, bilaterally expandable trial

ABSTRACT

Systems and methods for distracting an intervertebral disc space are provided. The systems use a staged, bilaterally expandable trial. The systems and methods of distracting an intervertebral space are provided in a manner that addresses the problem of subsidence. The method includes inserting the trial into the intervertebral space in a collapsed state and, once inserted, the trial is then used for distracting the intervertebral space using an expansion that includes a first stage and a second stage. The first stage includes expanding the trial laterally toward the peripheral zones of the top vertebral plate and the bottom vertebral plate, and the second stage includes expanding the trial vertically to distract the intervertebral space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Application No. 61/875,688,filed Sep. 9, 2013, which is hereby incorporated herein by reference inits entirety.

BACKGROUND

1. Field of the Invention

The teachings herein are directed to systems and methods for distractingan intervertebral disc space using a staged, bilaterally expandabletrial.

2. Description of the Related Art

Bone grafts are used in spinal fusion, for example, which is a techniqueused to stabilize the spinal bones, or vertebrae, and a goal is tocreate a solid bridge of bone between two or more vertebrae. The fusionprocess includes “arthrodesis”, which can be thought of as the mendingor welding together of two bones in a spinal joint space, much like abroken arm or leg healing in a cast. Spinal fusion may be recommendedfor a variety of conditions that might include, for example, aspondylolisthesis, a degenerative disc disease, a recurrent discherniation, or perhaps to correct a prior surgery.

Bone graft material is introduced for fusion and a fusion cage can beinserted to help support the disc space during the fusion process. Infact, fusion cages are frequently used in such procedures to support andstabilize the disc space until bone graft unites the bone of theopposing vertebral endplates in the disc space. A transforaminal lumbarinterbody fusion (TLIF), for example, involves placement of posteriorinstrumentation (screws and rods) into the spine, and the fusion cageloaded with bone graft can be inserted into the disc space. Bone graftmaterial can be pre-packed in the disc space or packed after the cage isinserted. TLIF can be used to facilitate stability in the front and backparts of the lumbar spine promoting interbody fusion in the anteriorportion of the spine. Fusion in this region can be beneficial, becausethe anterior interbody space includes an increased area for bone toheal, as well as to handle increased forces that are distributed throughthis area.

Unfortunately, therein lies a problem solved by the teachings providedherein. Currently available systems can be problematic in that themethods of introducing the fusion cage and bone graft material creates“subsidence” of the cage into the adjoining vertebrae, resulting in anarrowing of the formerly distracted disc space. This is because thecage is inserted near the middle of the endplate area which is softerthan the areas at or near the peripheral zone of the endplate, and whenit distracts, the cage actually sinks into the endplate creating thesubsidence problem. The problem remains with state-of-the-artdistraction instruments, such as the Medtronic SCISSOR JACK, paddletrials, or oversized trial shims (metallic wedges). Each of thesestate-of-the-art procedures introduce the distraction means narrowly (nowider than width of annulotomy) and then distract the intervertebralspace with a narrow foot print that ranges from about 8 mm to about 11mm wide.

Accordingly, and for at least the above reasons, those of skill in theart will appreciate distraction systems that facilitate an improvedplacement of distraction stresses across the verterbral endplates thatdefine the distracted intervertebral space. Such systems are providedherein, the systems configured to (i) effectively and selectively placethe distraction stresses in areas that include areas at or near theperipheral zones of the vertebral endplates to reduce the incidence ofsubsidence; (ii) reduce or eliminate the problem of failures resultingfrom subsidence; (iii) have a small maximum dimension of the trial in acollapsed state for a low-profile insertion into the annulus in aminimally-invasive manner, whether using only a unilateral approach or abilateral approach; (iv) laterally expand within the intervertebralspace to facilitate the effective and selective distribution ofdistraction stresses on the vertebral endplates; (v) vertically expandfor distraction of the intervertebral space; (vi) provide an expansionin the intervertebral space without contracting the system in length tomaintain a large footprint during the distraction process, distributingload over a larger area, including areas at or near the peripheral zonesof the vertebral endplates; and, (vii) serve as a measuring device forthe size of the intervebral space to facilitate selection of the size ofthe cage.

SUMMARY

The teachings herein are directed to systems and methods for distractingan intervertebral disc space using a staged, bilaterally expandabletrial. Generally, the teachings are directed to a method of distractingan intervertebral space in a manner that addresses the problem ofsubsidence. The teachings include obtaining a bilaterally expandabletrial that is configured to first expand laterally and then expandvertically to distract an intervertebral space having a top vertebralplate and a bottom vertebral plate. The trial is then inserted into theintervertebral space in a collapsed state. Once inserted, the trial thenused for distracting the intervertebral space using a staged, bilateralexpansion, the distracting including a first stage and a second stage.The first stage includes expanding the trial laterally toward theperipheral zones of the top vertebral plate and the bottom vertebralplate, and the second stage includes expanding the trial vertically todistract the intervertebral space.

As such, a staged, bilaterally-expandable trial for an intervertebralspace is provided. In some embodiments, the trial comprises abilaterally-expandable shell having a proximal region with an end, amid-region, a distal region with an end, and a lumen. The proximalregion can have a slider-guide, and the distal region can have abilaterally-expandable head with 4 subheads that include a first topbeam, a second top beam, a first bottom beam, and a second bottom beam.The mid-region can have 4 flex rods that include a first top flex rod, asecond top flex rod, a first bottom flex rod, and a second bottom flexrod, each of which operably attaches the slider-guide to it's respectivesubhead.

One or more beam stabilizers can be included stabilize and/or align thesubheads during operation of the device. A beam stabilizer, for example,can slidably translate, such that it is telescopic with respect to oneor both subheads between which it is operably attached to stabilizeand/or align the relationship between the subheads during operation ofthe device. In some embodiments, the beams can be stabilized withtranslatable, telescopic linear guides, such that the linear guide cantelescope within itself. For example, the first top beam can be operablyconnected to the second top beam with a top telescopic beam stabilizer,the first top beam can be operably connected to the second top beam witha top telescopic beam stabilizer, the first top beam can be operablyconnected to the first bottom beam with a first side telescopic beamstabilizer, the second top beam can be operably connected to the secondbottom beam with a second side telescopic beam stabilizer, and the firstbottom beam can be operably connected to the second bottom beam with abottom telescopic beam stabilizer. The beam stabilizer, or at least aportion thereof, can be fixably attached, or monolithically integral to,one or both beams between which it is operably connected or positionedin either a fixed or translatable configuration in the trial.

The trial can be expanded first laterally, and then vertically, usingany means known to one of skill. For example, the trial can alsocomprise a shim having a proximal region with an end; a mid-region; adistal region with an end; a central axis; a top surface with a firsttop-lateral surface and a second top-lateral surface; a bottom surfacewith a first bottom-lateral surface and a second bottom-lateral surface;a first side surface with a first top-side surface and a firstbottom-side surface; and, a second side surface with a second top-sidesurface and a second bottom-side surface. The shim can be configured fora proximal-to-distal axial translation in the lumen of the shell thatinduces a lateral force on the 4 subheads followed by a vertical forceon the 4 subheads for a staged, bilateral expansion in vivo thatincludes a lateral expansion of the head followed by a verticalexpansion of the head in an intervertebral space having a top vertebralendplate, a bottom vertebral endplate, and an annulus.

The head of the trial can be configured with a proximal portion havingan end; a distal portion having an end; and, a central shell axis of theexpanded state; the head adapted for slidably-engaging with the shim invivo following placement of the trial in the intervertebral spacethrough the annular opening, the slidably-engaging includingaxially-translating the shim in the lumen of the shell from the proximalend of the lumen toward the distal end of the lumen in vivo; thetranslating including keeping the central shim axis at leastsubstantially coincident with the central shell axis during thetranslating.

The teachings are also directed to systems that include means forapplying an axial proximal-to-distal force on a shim that expands thetrial. In some embodiments, the proximal end of the shim can beconfigured to receive the axial proximal-to-distal force through anactuation bar for the axial translation, the actuation bar having aproximal portion with a proximal end, a distal portion with a distalend, and configured to transfer the axial proximal-to-distal force tothe shim through the slider-guide.

The systems can include an actuation means operably attached to theproximal end of the actuation bar to transfer the axialproximal-to-distal force to the shim through the distal end of theactuation bar. In some embodiments, the actuation bar receives the axialproximal-to-distal force from an actuation screw that can be operablyattached to the proximal end of the actuation bar to transfer the forceto the shim through the distal end of the actuation bar. The systems canfurther comprise a retractable retention plunger configured forretaining the trial in the collapsed state and releasing the trial forexpansion into the expanded state.

The head of the trial can have a collapsed dimension that facilitatesinsertion to the intervertebral space and an expanded dimension thatfacilitates the desired lateral expansion and vertical expansion in theintervertebral space. In some embodiments, the head of the trial canhave a collapsed state with a transverse cross-section having a maximumdimension ranging from 5 mm to 18 mm for placing the frame in anintervertebral space through an annular opening for expansion in theintervertebral space. And, in some embodiments, the head of the trialcan have an expanded state with a transverse cross-section having amaximum dimension ranging from 6.5 mm to 28 mm, 7.5 mm to 28 mm, 8.5 mmto 28 mm, 6.5 mm to 27 mm, 6.5 mm to 25 mm, 6.5 mm to 23 mm, 6.5 mm to21 mm, 6.5 mm to 19 mm, 6.5 mm to 18 mm, or any range therein inincrements of 1 mm, in the intervertebral space. In some embodiments,the shim can have a transverse cross-section with a maximum dimensionranging from 5 mm to 18 mm, 6 mm to 18 mm, 7 mm to 18 mm, 5 mm to 15 mm,5 mm to 16 mm, 5 mm to 17 mm, or any range therein in increments of 1mm, for translating the shim in the lumen of the shell.

In some embodiments, the shim can have a horizontal wedge configured tolaterally-expand the trial, and a vertical wedge configured tovertically-expand the trial. In some embodiments, the shim can have atop wedge configured to laterally-expand the first top beam away fromthe second top beam, a bottom wedge configured to laterally-expand thefirst bottom beam away from the second bottom beam, a first side wedgeconfigured to vertically-expand the first top beam away from the firstbottom beam, and a second side wedge configured to vertically-expand thesecond top beam away from the second bottom beam. In some embodiments,the proximal portion of the first top beam and the proximal portion ofthe second top beam can be configured to complement the top wedge at theonset of the lateral expansion during the proximal-to-distal axialtranslation; and, the proximal portion of the first bottom beam and theproximal portion of the second bottom beam can be configured tocomplement the bottom wedge at the onset of the lateral expansion duringthe proximal-to-distal axial translation. In some embodiments, thedistance, D_(STAGING), between the onset of the lateral expansion andthe onset of the vertical translation can range from 2 mm to 10 mm.

In some embodiments, the proximal portion of the first top beam and theproximal portion of the first bottom beam can be configured tocomplement the first side wedge during the proximal-to-distal axialtranslation for the vertical expansion; and, the proximal portion of thesecond top beam and the proximal portion of the second bottom beam canbe configured to complement the second side wedge during theproximal-to-distal axial translation for the vertical expansion.

In some embodiments, the first top beam can include a proximal portionhaving an end, a distal portion having an end, and a central axis; thefirst top beam configured for contacting a first top chamfer of the shimin the expanded state, the central axis of the first top beam at leastsubstantially on (i) a top plane containing the central axis of thefirst top beam and the central axis of a second top beam and (ii) afirst side plane containing the central axis of the first top beam andthe central axis of a first bottom beam. Likewise, the second top beamcan include a proximal portion having an end, a distal portion having anend, and a central axis; the second top beam configured for contacting asecond top chamfer of the shim in the expanded state, the central axisof the second top beam at least substantially on (i) the top plane and(ii) a second side plane containing the central axis of the second topbeam and the central axis of a second bottom beam. Likewise, the firstbottom beam can include a proximal portion having an end, a distalportion having an end, and a central axis; the first bottom beamconfigured for contacting a first bottom chamfer of the shim in theexpanded state, the central axis of the first bottom beam at leastsubstantially on (i) a bottom plane containing the central axis of thefirst bottom beam and the central axis of a second top beam and (ii) thefirst side plane. Moreover, the second bottom beam can include aproximal portion having an end, a distal portion having an end, and acentral axis; the second bottom beam configured for contacting a secondbottom chamfer of the shim in the expanded state, the central axis ofthe second bottom beam being at least substantially on (i) the bottomplane and (ii) a second side plane containing the central axis of thesecond bottom beam and the second top beam.

In some embodiments, the first top beam can include a proximal portionhaving an end, a distal portion having an end, and a central axis; thefirst top beam configured for contacting a first top-lateral surface ofthe shim and a first top-side surface of the shim in the expanded state,the central axis of the first top beam at least substantially on (i) atop plane containing the central axis of the first top beam and thecentral axis of a second top beam and (ii) a first side plane containingthe central axis of the first top beam and the central axis of a firstbottom beam. Likewise, the second top beam can include a proximalportion having an end, a distal portion having an end, and a centralaxis; the second top beam configured for contacting the secondtop-lateral surface of the shim and the second top-side surface of theshim in the expanded state, the central axis of the second top beam atleast substantially on (i) the top plane and (ii) a second side planecontaining the central axis of the second top beam and the central axisof a second bottom beam. Likewise, the first bottom beam can include aproximal portion having an end, a distal portion having an end, and acentral axis; the first bottom beam configured for contacting the firstbottom-lateral surface of the shim and the first bottom-side surface ofthe shim in the expanded state, the central axis of the first bottombeam at least substantially on (i) a bottom plane containing the centralaxis of the first bottom beam and the central axis of a second top beamand (ii) the first side plane. Moreover, the second bottom beam caninclude a proximal portion having an end, a distal portion having anend, and a central axis; the second bottom beam configured forcontacting the second bottom-lateral surface of the shim and the secondbottom-side surface of the shim in the expanded state, the central axisof the second bottom beam being at least substantially on (i) the bottomplane and (ii) a second side plane containing the central axis of thesecond bottom beam and the second top beam.

In some embodiments, the shim can comprise a lateral-expansion wedgewith angle θ_(L) ranging from 10° to 30° and a vertical-expansion wedgewith angle θ_(V) ranging from 30° to 50°, the apex of thelateral-expansion wedge and the apex of the vertical-expansion wedgeeach at least substantially on a single plane that is orthogonal to thecentral axis of the shim, and the ratio of θ_(V):θ_(L) ranges from1:1.25 to 1:4 to stage the bilateral expansion of the head.

In some embodiments, the shim can comprise a lateral-expansion wedgewith angle θ_(L) ranging from 10° to 90° and a vertical-expansion wedgewith angle θ_(V) ranging from 10° to 90°, the apex of thelateral-expansion wedge on a first plane and the apex of the verticalexpansion wedge on a second plane, both the first plane and the secondplane being orthogonal to the central axis of the shim and separated onthe central axis at a distance ranging from 2 mm to 10 mm to stage thebilateral expansion of the head.

The shell can be formed using any method of construction known to one ofskill, for example, multi-component or single unit. In some embodiments,the shell can be a single-unit formed from a single body of material,and the slider-guide, head, and flex rods can be monolithicallyintegral.

Accordingly, the teachings include a method of distracting anintervertebral space using the trials taught herein. In someembodiments, the method can comprise creating a point of entry into anintervertebral disc, the intervertebral disc having a nucleus pulposussurrounded by an annulus fibrosis, and the point of entry having themaximum lateral dimension created through the annulus fibrosis. Themethods can include removing the nucleus pulposus from within theintervertebral disc through the point of entry, leaving theintervertebral space for expansion of the head of the trial within theannulus fibrosis, the intervertebral space having the top vertebralplate and the bottom vertebral plate. The methods can include insertingthe head in the collapsed state through the point of entry into theintervertebral space; and, distracting the intervertebral space using astaged, bilateral expansion that includes a first stage and a secondstage. The distracting can include a first stage and a second stage, thefirst stage including expanding the head laterally toward the peripheralzones of the top vertebral plate and the bottom vertebral plate; and,the second stage including expanding the head vertically to distract theintervertebral space, the pressure for the expansion occurringpreferably, and at least primarily, at or near the peripheral zones ofthe top vertebral plate and the bottom vertebral plate. In someembodiments, the lateral dimension of the point of entry ranges fromabout 5 mm to 18 mm, 6 mm to 18 mm, 7 mm to 18 mm, 5 mm to 15 mm, 5 mmto 16 mm, 5 mm to 17 mm, or any range therein in increments of 1 mm.

In some embodiments, the distracting includes selecting an amount oflateral expansion independent of an amount of vertical expansion. And,in some embodiments, the distracting includes measuring the amount oflateral expansion independent of the amount of vertical expansion.

In some embodiments, the distracting includes as a first stage oflateral expansion, inserting a top wedge into the head between the firsttop beam and the second top beam, the top wedge composing a portion ofthe shim and configured to laterally-expand the first top beam away fromthe second top beam; and, inserting a bottom wedge into the head betweenthe first bottom beam and the second bottom beam, the bottom wedgeconfigured to laterally-expand the first bottom beam away from thesecond bottom beam. And, as a second stage of expansion, inserting afirst side wedge into the head between the first top beam and the firstbottom beam, the first side wedge configured to laterally-expand thefirst top beam away from the first bottom beam; and, inserting a secondside wedge into the head between the second top beam and the secondbottom beam, the second side wedge configured to laterally-expand thesecond top beam away from the second bottom beam.

In some embodiments, the distracting includes selecting a shim having alateral-expansion wedge with angle θ_(L) ranging from 10° to 30° and avertical-expansion wedge with angle θ_(V) ranging from 30° to 50°, theapex of the lateral-expansion wedge and the apex of thevertical-expansion wedge each at least substantially on a single planethat is orthogonal to the central axis of the shim, and the ratio ofθ_(V):θ_(L) ranges from 1:1.25 to 1:4 to stage the bilateral expansionof the head.

In some embodiments, the distracting includes selecting a shim having alateral-expansion wedge with angle θ_(L) ranging from 10° to 90° and avertical-expansion wedge with angle θ_(V) ranging from 10° to 90°, theapex of the lateral-expansion wedge on a first plane and the apex of thevertical expansion wedge on a second plane, both the first plane and thesecond plane being orthogonal to the central axis of the shim andseparated on the central axis at a distance ranging from 2 mm to 10 mmto stage the bilateral expansion of the head.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B illustrate a sketch of an endplate of a vertebral bodyand a representative photograph of an intervertebral space using acadaver intervertebral body and disc, according to some embodiments.

FIG. 2 illustrates a process of using a staged, bilaterally-expandabletrial for distracting an intervertebral space, according to someembodiments.

FIGS. 3A-3D illustrate a staged, bilaterally-expandable trial, accordingto some embodiments.

FIGS. 4A-4D illustrate a shim for the staged, bilaterally expandingtrial, according to some embodiments.

FIG. 5 illustrates the concept of the staged, bilateral expansion of thetrial, according to some embodiments.

FIG. 6 illustrates a trial system for a staged, bilateral expansion ofthe trial in an intervertebral space, according to some embodiments.

FIGS. 7A and 7B illustrate a trial system with an expansion gauge and aretractable retention plunger for retaining the trial prior to a staged,bilateral expansion of the trial in an intervertebral space, accordingto some embodiments.

FIGS. 8A-8D illustrate a staged, bilaterally-expandable trial with beamstabilizers that telescope within themselves, according to someembodiments.

FIGS. 9A-9D illustrate a staged, bilaterally-expandable trial with beamstabilizers that telescope with one or both subheads having acounter-bore, according to some embodiments.

DETAILED DESCRIPTION OF THE INVENTION

Systems and methods for distracting an intervertebral disc space using astaged, bilaterally expandable trial are provided. Generally speaking, asystem for distracting an intervertebral disc space using a staged,bilaterally expandable trial is provided. Generally, the teachings aredirected to a method of distracting an intervertebral space in a mannerthat addresses the problem of subsidence by selectively applyingdistraction forces to stronger portions of the vertebral endplates ofthe intervertebral space. It should be appreciated that the term “trial”can be used interchangeably with the term “distractor” in manyembodiments.

FIGS. 1A and 1B illustrate a sketch of an endplate of a vertebral bodyand a representative photograph of an intervertebral space using acadaver intervertebral body and disc, according to some embodiments.This illustration provides a reference to discuss the state-of-the-artmethods of introducing the fusion cage and bone graft material whichcreate “subsidence” of the cage into the adjoining vertebrae, resultingin a narrowing of the formerly distracted disc space. As shown in FIG.1A, the vertebral body 100 has an endplate 105 with a mid-region 115 anda peripheral zone 125. The problem occurs because the cage is typicallyinserted at or near the mid-region 115 which is softer than the areas ator near the peripheral zone 125 of the endplate 105, and when itdistracts, the cage actually sinks into the endplate 105 creating thesubsidence problem. The problem remains with state-of-the-artdistraction instruments, such as the Medtronic SCISSOR JACK, paddletrials, or oversized trial shims (metallic wedges). Each of thesestate-of-the-art procedures introduce the distraction means narrowly (nowider than width of annulotomy) and then distract the intervertebralspace with a narrow foot print that ranges, for example, from about 8 mmto about 11 mm wide. FIG. 1B illustrates a cadaver intervertebral body150, and the annulus 153 that surrounds the intervertebral space 155that receives the trial.

In some embodiments, the phrase “at or near the peripheral zone” of avertebral endplate can be interpreted as meaning “at least substantiallyaway from the central portion of the area of the vertebral endplate. Adistraction pressure can be applied, for example, at least substantiallyaway from the central portion where greater than 30%, greater than 35%,greater than 40%, greater than 45%, greater than 50%, greater than 55%,greater than 60%, greater than 65%, greater than 70%, greater than 75%,greater than 80%, greater than 85%, greater than 90%, greater than 95%,or more of the surface area of a pair of subheads that is facing, or insome embodiments in contact or potential contact with, their respectiveendplate outside of the central portion. In some embodiments, the“central portion” can be defined as a scaled-down area on the surface ofthe endplate, and thus sharing a plane with the surface of the endplate,sharing a center-point on the plane, and sharing the same general shapeas the total area of the endplate, albeit scaled-down. As such, anoverlay of the central portion that is placed on the total area with thesame orientation, and placed carefully such that the center-point of thecentral portion is shared/concentric with the center-point of the totalarea, leaves a “remaining area” or “remainder” around the periphery ofthe total area that can be defined, for example, as either a “peripheralzone” in some embodiments, or “at-or-near the peripheral zone,” in someembodiments. The following table shows a hypothetical relationshipbetween the radius and the area of a hypothetical endplate model usingfor simplicity a circular area having a diameter of 25 mm.

scale (fraction diameter radius area of total area) (mm) (mm)(mm){circumflex over ( )}2 1.00 25.00 12.50 490.88 total area 0.70 10.46343.62 Scaled 0.60 9.68 294.53 Scaled 0.50 8.84 245.44 Scaled 0.40 7.91196.35 Scaled 0.30 6.85 147.26 Scaled 0.20 5.59 98.18 Scaled 0.10 3.9549.09 Scaled

Interestingly, a central portion of the hypothetical circular areahaving area based on a radius of 6.85 mm, which is about 55% of thetotal radius provides only 30% of the total area. As such, if thecentral portion amounts to only about 50% of the total area, it usesabout two-thirds of the radius of the total area, leaving a radialdimension for the peripheral zone that is about 3.66 mm wide for thehypothetical endplate having the diameter of 25 mm. In some embodiments,the central portion can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%,55%, 60%, 65%, 70%, or any percentage therein increments of 1%, of thetotal area. In some embodiments, the peripheral zone can have a radialdimension, or radial width, that is 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm,8 mm, or any 0.1 mm increment therein. It should be appreciated that theradial dimension, or radial width, is the thickness of the peripheralzone area that circumscribes the periphery of the endplate as shown inFIG. 1, 125, and further described above qualitatively with respect tothe remainder of the overlay of the central portion on the total area.One of skill will appreciate that a peripheral zone does not have to beuniform, and that the teachings provided herein to define the peripheralzone, or the area at-or-near the peripheral zone, are taught to furtherclarify boundaries of some embodiments by distinguishing both aconfiguration and function of the trials and systems taught herein fromthe current state-of-the-art. As such, it should be appreciated that thetrials can be further configured to have a contour, whether laterally,vertically, or both laterally and vertically, that is at leastsubstantially complementary to the areas within the peripheral zone, orat-or-near the peripheral zone, during operation of the trials providedherein. For example, the trial can have a linear, curved, or curvalinearlateral surface; a flat or convex vertical surface; or, some combinationthereof, upon expansion to provide a shape that is at leastsubstantially complementary to the peripheral zone of the endplates uponexpansion.

FIG. 2 illustrates a process of using a staged, bilaterally-expandabletrial for distracting an intervertebral space, according to someembodiments. The method 200 of distracting an intervertebral space caninclude, for example, obtaining a bilaterally expandable trial that isconfigured to first expand laterally and then expand vertically todistract an intervertebral space having a top vertebral plate and abottom vertebral plate. The method 200 includes creating 205 a point ofentry into an intervertebral disc and removing 210 the nucleus pulposusfrom within the intervertebral disc to create an intervertebral space.The method further includes inserting 215 the trial into theintervertebral space in a collapsed state. Once inserted, the trial thenused for distracting 220 the intervertebral space using a staged,bilateral expansion, the distracting including a first stage and asecond stage. The first stage includes laterally expanding 225 the trialto a position at or near the peripheral zones of the top vertebral plateand the bottom vertebral plate, and the second stage includes verticallyexpanding 230 the trial at or near the peripheral zones of the topvertebral plate and the bottom vertebral plate to distract theintervertebral space while avoid the problem of subsidence.

FIGS. 3A-3D illustrate a staged, bilaterally-expandable trial, accordingto some embodiments. As shown in FIG. 3A, a top view of the trial 300,the trial 300 comprises a bilaterally-expandable shell having a proximalregion 301 with an end 302, a mid-region 303, a distal region 305 withan end 306, and a lumen 307. As shown in FIG. 3B, the proximal region301 can have a slider-guide 310, and the distal region 305 can have abilaterally-expandable head 315 with 4 subheads 316,317,318,319 thatinclude a first top beam 316, a second top beam 317, a first bottom beam318, and a second bottom beam 319. The mid-region can have 4 flex rods321,322,323,324 that include a first top flex rod 321, a second top flexrod 322, a first bottom flex rod 323, and a second bottom flex rod 324,each of which operably attaches the slider-guide 310 to it's respectivesubhead. As shown in FIG. 3C, the end 306 of the distal region can betapered or otherwise round, configured in the collapsed state in someembodiments, for example, as a bullet-nosed tip to avoid damage to theinner annulus during the distraction procedure. As shown in FIG. 3D, aside view of the trial 300, and comparing to FIG. 3A, the ratio of θ_(V)to θ_(L) is 1:2 in this embodiment for a staged bilateral expansion ofthe trial. The example dimensions shown in FIGS. 3A-3D are in inches.

In some embodiments, the rods can range from 2 cm to 4 cm in length and0.5 mm to 2 mm in thickness. In some embodiments, the rods can be 1 mmwide by 1 mm thick and have a length of 2.5 cm.

In some embodiments, the shell can be wider at the head than the regionproximal to the head. In some embodiments, the shell can be taller atthe head than the region proximal to the head.

The trial can be expanded first laterally, and then vertically, usingany means known to one of skill. FIGS. 4A-4D illustrate a shim for thestaged, bilaterally expanding trial, according to some embodiments. Asshown in FIGS. 4A and 4B, the trial can also comprise a shim 400 havinga proximal region 401 with an end 402; a mid-region 403; a distal region405 with an end 406; a central axis 409; a top surface 411 with a firsttop-lateral surface 412 and a second top-lateral surface 413; a bottomsurface 415 with a first bottom-lateral surface 416 and a secondbottom-lateral surface 417; a first side surface 419 with a firsttop-side surface 420 and a first bottom-side surface 421; and, a secondside surface 425 with a second top-side surface 426 and a secondbottom-side surface 427. The shim can be configured for aproximal-to-distal axial translation 444 in the lumen of the shell thatinduces a lateral force on the 4 subheads followed by a vertical forceon the 4 subheads for a staged, bilateral expansion in vivo thatincludes a lateral expansion of the head followed by a verticalexpansion of the head in an intervertebral space having a top vertebralendplate, a bottom vertebral endplate, and an annulus.

The head of the trial can be configured with a proximal portion havingan end; a distal portion having an end; and, a central shell axis of theexpanded state; the head adapted for slidably-engaging with the shim invivo following placement of the trial in the intervertebral spacethrough the annular opening, the slidably-engaging includingaxially-translating the shim in the lumen of the shell from the proximalend of the lumen toward the distal end of the lumen in vivo; thetranslating including keeping the central shim axis at leastsubstantially coincident with the central shell axis during thetranslating.

In some embodiments, the shim has a cross-shaped cross-section which isformed by the crossing of a vertical wedge and a lateral wedge. Bothwedges can taper down to an edge at the distal end. When the shim slidesdistally relative to the shell, it can push against the inner chamferson the subheads to move the subheads away from each other to expand theshell head. When the head expands, the subheads are pushed outward andflex the respective rods outward. When the shim is pulled back, the headcollapses because the rods flex back in. Additionally, a coil spring canbe wrapped around an outer transverse groove on the head to further helpto pull the subheads together when the shim is pulled back. An elasticband (silicone) can be used rather than coil spring. The shell-shimassembly can be designed such that the lateral expansion wedge engageswith the chamfers on the subheads before the vertical expansion wedgeengages so that the head expands laterally before it expands vertically.In some embodiments, this can be achieved by having the lateralexpansion chamfers (angled relative to vertical plane along long axis ofdevice) angled more from the long axis than the vertical expansionchamfers. In one embodiment, the lateral expansion chamfers are 20degrees from long axis and the vertical expansion chamfers are 10degrees from the axis. In one embodiment, the bevels on the wedges areparallel to the chamfers on the subheads. In some embodiments, thebevels on the lateral expansion wedge can be advanced beyond the lateralexpansion chamfers before the vertical expansion wedge engages thevertical expansion chamfers on the subheads. Once the bevels on thelateral expansion wedge is advanced beyond the chamfer, there is no morehead expansion as the shim is advanced further distally. As such, theshim can continue to be advanced distally to expand the head verticallywithout further lateral expansion.

In some embodiments, the subheads can be 4.5 mm thick laterally and thelateral expansion wedge tapers up to 4 mm wide to allow for lateralexpansion from 9 mm to 13 mm. The collapsed thickness of the head in anydirection can be the sum of the thicknesses of the subheads in thatdirection, and the maximum amount of expansion can be the maximumthickness of the wedge. In some embodiments, the subheads can be 3.35 mmin the vertical direction and the vertical expansion wedges can be 4.3mm tall to allow for vertical expansion from 6.7 mm to 11 mm. In someembodiments, the subheads can be 4 mm tall in the vertical direction andthe vertical expansion wedges can be 6 mm tall to allow for verticalexpansion from 8 mm to 14 mm.

In some embodiments, the shim can have a tail that extends 2 cm to 4 cmlong proximal from the wedge part and a rectangular cross section thatis 2 mm to 5 mm thick. The tail can be configured to slide along arectangular hole in the slider guide. This construct can be adapted tolimit the movement of the wedges to the long axis direction. In someembodiments, the shell rods can be flush with a groove formed by anintersection between the vertical and lateral wedges to help keep theassembly stable for insertion into the disc. In some embodiments, thevertical wedges can be flush with the vertical chamfers on the subheadsin the collapsed state to further stabilize the subheads from movementin the lateral direction for insertion into the disc space.

One of skill will also appreciate having a method of designing the shapeof the head upon expansion. In some embodiments, for example, it may bebeneficial for the distal expansion of the head to be larger than theproximal expansion of the head to account for a lordosis in the subject.Or, in some embodiments, for example, it may be considered beneficialfor the expanded head to have a convexity in the subheads that applies apressure to either endplate. As such, in some embodiments, the expandingincludes selecting a shim configured to vertically expand the distal endof the cage more than the proximal end of the cage. Or, in someembodiments, the expanding includes selecting a shim configured tocreate a convex surface on the top surface of the top wall, for example,to at least substantially complement the concavity of the respective topvertebral plate, and/or the bottom surface of the bottom wall to atleast substantially complement the concavity of the respective bottomvertebral plate. Or, in some embodiments, the expanding includesselecting a shim configured to laterally expand the distal end of thecage more than the proximal end of the cage.

One of skill will appreciate that the trial or the shim can befabricated using any desirable material having the requisite materialcharacteristics of strength, flexibility, biocompatibility, and thelike. In some embodiments, the shell and the shim can be fabricated fromstainless steel but can be made of any metal or hard plastics such asULTEM and PEEK.

The head of the trial can have a collapsed dimension that facilitatesinsertion to the intervertebral space and an expanded dimension thatfacilitates the desired lateral expansion and vertical expansion in theintervertebral space. In some embodiments, the head of the trial canhave a collapsed state with a transverse cross-section having a maximumdimension ranging from 5 mm to 18 mm, 6 mm to 18 mm, 7 mm to 18 mm, 5 mmto 15 mm, 5 mm to 16 mm, 5 mm to 17 mm, or any range therein inincrements of 1 mm, for placing the frame in an intervertebral spacethrough an annular opening for expansion in the intervertebral space.And, in some embodiments, the head of the trial can have an expandedstate with a transverse cross-section having a maximum dimension rangingfrom 6.5 mm to 28 mm, 7.5 mm to 28 mm, 8.5 mm to 28 mm, 6.5 mm to 27 mm,6.5 mm to 25 mm, 6.5 mm to 23 mm, 6.5 mm to 21 mm, 6.5 mm to 19 mm, 6.5mm to 18 mm, or any range therein in increments of 1 mm, in theintervertebral space. In some embodiments, the shim can have atransverse cross-section with a maximum dimension ranging from 5 mm to18 mm for translating the shim in the lumen of the shell.

In some embodiments, the shim can have a horizontal wedge, HW,configured to laterally-expand the trial, and a vertical wedge, VW,configured to vertically-expand the trial. In some embodiments, the shimcan have a top wedge configured to laterally-expand the first top beamaway from the second top beam, a bottom wedge configured tolaterally-expand the first bottom beam away from the second bottom beam,a first side wedge configured to vertically-expand the first top beamaway from the first bottom beam, and a second side wedge configured tovertically-expand the second top beam away from the second bottom beam.In some embodiments, the proximal portion of the first top beam and theproximal portion of the second top beam can be configured to complementthe top wedge at the onset of the lateral expansion during theproximal-to-distal axial translation; and, the proximal portion of thefirst bottom beam and the proximal portion of the second bottom beam canbe configured to complement the bottom wedge at the onset of the lateralexpansion during the proximal-to-distal axial translation.

FIG. 5 illustrates the concept of the staged, bilateral expansion of thetrial, according to some embodiments. As shown in FIG. 5, the distance,D_(STAGING), between the onset of the lateral expansion 533 and theonset of the vertical expansion 543 can range from 2 mm to 10 mm, and isthe axial proximal-to-distal distance traveled by the shim in the stagedexpansion.

In some embodiments, the proximal portion of the first top beam and theproximal portion of the first bottom beam can be configured tocomplement the first side wedge during the proximal-to-distal axialtranslation for the vertical expansion; and, the proximal portion of thesecond top beam and the proximal portion of the second bottom beam canbe configured to complement the second side wedge during theproximal-to-distal axial translation for the vertical expansion.

In some embodiments, the first top beam 516 can include a proximalportion having an end, a distal portion having an end, and a centralaxis 516 a; the first top beam 516 configured for contacting a first topchamfer 555 (lateral and vertical) of the shim in the expanded state,the central axis 516 a of the first top beam 516 at least substantiallyon (i) a top plane containing the central axis 516 a of the first topbeam 516 and the central axis 517 a of a second top beam 517 and (ii) afirst side plane containing the central axis 516 a of the first top beam516 and the central axis 518 a of a first bottom beam 518. Likewise, thesecond top beam 517 can include a proximal portion having an end, adistal portion having an end, and a central axis 517 a; the second topbeam 517 configured for contacting a second top chamfer 566 (lateralshown, vertical not shown) of the shim in the expanded state, thecentral axis 517 a of the second top beam 517 at least substantially on(i) the top plane and (ii) a second side plane containing the centralaxis 517 a of the second top beam 517 and the central axis 519 a of asecond bottom beam 519. Likewise, the first bottom beam 518 can includea proximal portion having an end, a distal portion having an end, and acentral axis 518 a; the first bottom beam 518 configured for contactinga first bottom chamfer 577 (vertical shown, lateral not shown) of theshim in the expanded state, the central axis 518 a of the first bottombeam 518 at least substantially on (i) a bottom plane containing thecentral axis 518 a of the first bottom beam 518 and the central axis 517a of a second top beam 517 and (ii) the first side plane. Moreover, thesecond bottom beam 519 (not shown) can include a proximal portion havingan end, a distal portion having an end, and a central axis 519 a; thesecond bottom beam 519 configured for contacting a second bottom chamfer(not shown) of the shim in the expanded state, the central axis 519 a ofthe second bottom beam 519 being at least substantially on (i) thebottom plane and (ii) a second side plane containing the central axis519 a of the second bottom beam 519 and the central axis 517 a of thesecond top beam 517.

In some embodiments, the first top beam can include a proximal portionhaving an end, a distal portion having an end, and a central axis; thefirst top beam configured for contacting a first top-lateral surface ofthe shim and a first top-side surface of the shim in the expanded state,the central axis of the first top beam at least substantially on (i) atop plane containing the central axis of the first top beam and thecentral axis of a second top beam and (ii) a first side plane containingthe central axis of the first top beam and the central axis of a firstbottom beam. Likewise, the second top beam can include a proximalportion having an end, a distal portion having an end, and a centralaxis; the second top beam configured for contacting the secondtop-lateral surface of the shim and the second top-side surface of theshim in the expanded state, the central axis of the second top beam atleast substantially on (i) the top plane and (ii) a second side planecontaining the central axis of the second top beam and the central axisof a second bottom beam. Likewise, the first bottom beam can include aproximal portion having an end, a distal portion having an end, and acentral axis; the first bottom beam configured for contacting the firstbottom-lateral surface of the shim and the first bottom-side surface ofthe shim in the expanded state, the central axis of the first bottombeam at least substantially on (i) a bottom plane containing the centralaxis of the first bottom beam and the central axis of a second top beamand (ii) the first side plane. Moreover, the second bottom beam caninclude a proximal portion having an end, a distal portion having anend, and a central axis; the second bottom beam configured forcontacting the second bottom-lateral surface of the shim and the secondbottom-side surface of the shim in the expanded state, the central axisof the second bottom beam being at least substantially on (i) the bottomplane and (ii) a second side plane containing the central axis of thesecond bottom beam and the second top beam.

The selection and arrangement of the wedges and angles can be selectedto stage the expansion of the trial in the lateral and verticaldirections. In some embodiments, the shim can comprise alateral-expansion wedge with angle θ_(L) ranging from 10° to 30° and avertical-expansion wedge with angle θ_(V) ranging from 30° to 50°, theapex of the lateral-expansion wedge and the apex of thevertical-expansion wedge each at least substantially on a single planethat is orthogonal to the central axis of the shim, and the ratio ofθ_(V):θ_(L) ranges from 1:1.25 to 1:4 to stage the bilateral expansionof the head.

In some embodiments, the shim can comprise a lateral-expansion wedgewith angle θ_(L) ranging from 10° to 90° and a vertical-expansion wedgewith angle θ_(V) ranging from 10° to 90°, the apex of thelateral-expansion wedge on a first plane and the apex of the verticalexpansion wedge on a second plane, both the first plane and the secondplane being orthogonal to the central axis of the shim and separated onthe central axis at a distance ranging from 2 mm to 10 mm to stage thebilateral expansion of the head.

The shell can be formed using any method of construction known to one ofskill, for example, multi-component or single unit. In some embodiments,the shell can be a single-unit formed from a single body of material,and the slider-guide, head, and flex rods can be monolithicallyintegral.

In some embodiments, each subhead can have a shape of a rectangular barwith a tapered tip on the outside surface and chamfers on the innersurfaces. The subheads can be located near the corners of the distal endof the trial. When collapsed for insertion, the head can be 6 mm to 9 mmin height by 6 mm to 10 mm in width, in some embodiments. Moreover, thehead can expand in some embodiments to 16 mm in height to 16 mm inwidth. In some embodiments, the head can expand from 6.7 mm to 11 mm inheight and from 9 mm 13 mm in width. In some embodiments, the head canexpand from 8 mm to 14 mm height and from 9 mm to 13 mm in width. Insome embodiments, the length of the head can range from 20 mm to 60 mm,20 mm to 50 mm, 20 mm to 40 mm, 25 mm to 45 mm, 25 mm to 55 mm, or anyrange therein increments of 1 mm.

In some embodiments, the trial can have a means for retaining thecollapsed state, such as an elastic means. The elastic means can be, forexample, a coil spring or an elastic silicone band. The means forretaining can circumscribe the outer circumference of the subheads, andcan be further affixed to the assembly using a transverse groove,helping to pull the subheads together when the shim is pulled in thedistal-to-proximal direction.

FIG. 6 illustrates a trial system for a staged, bilateral expansion ofthe trial in an intervertebral space, according to some embodiments. Thetrial system 600 includes the trial 605, the shim 610, a guide tube orbarrel 615 to help guide the trial 605 into the intervertebral space, anactuation bar 620, a threaded connector 625, a handle 630, an actuatorscrew 635, an actuator knob 640 to actuate the actuator screw 635 toapply the axial proximal-to-distal force, F_(PD), and a stop block 645to hold the actuator knob in place against the counter force, −F_(PD).

It should be appreciated that the systems can also include any knownmeans for applying an axial proximal-to-distal force on a shim thatexpands the trial. In some embodiments, the proximal end of the shim canbe configured to receive the axial proximal-to-distal force through theactuation bar for the axial translation, the actuation bar having aproximal portion with a proximal end, a distal portion with a distalend, and configured to transfer the axial proximal-to-distal force tothe shim through the slider-guide.

The systems can include such an actuation means operably attached to theproximal end of the actuation bar 620 to transfer the axialproximal-to-distal force F_(PD) to the shim 610 through the distal endof the actuation bar 620. In some embodiments, the actuation bar 620receives the axial proximal-to-distal force from the actuator screw 635that can be operably attached to the proximal end of the actuation bar620 to transfer the force to the shim 619 through the distal end of theactuation bar 620.

FIGS. 7A and 7B illustrate a trial system with an expansion gauge and aretractable retention plunger for retaining the trial prior to a staged,bilateral expansion of the trial in an intervertebral space, accordingto some embodiments. FIG. 7A provides an exploded view of the assemblyof the system 700. The system 700 includes the trial 705, the shim 710,a guide tube or barrel 715 to help guide the trial 705 into theintervertebral space. The system 700 also includes an actuation bar 720,a push rod 727, a handle 730, an actuator screw 735, an actuator knob740 to actuate the actuator screw 635 to apply the axialproximal-to-distal force, F_(PD), and a stop block 745 to hold theactuator knob 740 in place against the counter force, −F_(PD). The trial705

The systems can further comprise a retractable retention plungerconfigured for retaining the trial in the collapsed state and releasingthe trial for expansion into the expanded state. A retractable retentionplunger 760, for example, can also be included with a handle 763 and aretainer 767 for retaining the trial 705 in a collapsed state, theplunger functioning to retain the trial 705 by moving itproximal-to-distal 771 PD; and, to release the trial 705 by moving itdistal-to-proximal 771DP. The system can also include an expansion gauge750 to provide a measure of intervertebral expansion and contractionrealized when turning 777 the actuator knob 740 clockwise orcounterclockwise. The expansion occurs, for example, through an axialproximal-to-distal movement 779PD of the shim 710 into the trial 705.FIG. 7B shows the system assembled with the plunger 760 function toretain the trial 705 in the collapsed state. The trial 705 can beexpanded, for example, by pulling the plunger handle 763 in adistal-to-proximal direction for a distal-to-proximal movement 771DP ofthe retainer 767 to release the trial 705 for the expansion. Theexpansion is then obtained by turning the knob 740 to obtain the axialproximal-to-distal movement 779PD of the shim 710 into the trial 705.

One or more beam stabilizers can be included stabilize and/or align thesubheads during operation of the device. A beam stabilizer, for example,can slidably translate, such that it is telescopic with respect to oneor both subheads between which it is operably attached to stabilizeand/or align the relationship between the subheads during operation ofthe device. In some embodiments, the beams can be stabilized withtranslatable, telescopic linear guides, such that the linear guide cantelescope within itself. For example, the first top beam can be operablyconnected to the second top beam with a top telescopic beam stabilizer,the first top beam can be operably connected to the second top beam witha top telescopic beam stabilizer, the first top beam can be operablyconnected to the first bottom beam with a first side telescopic beamstabilizer, the second top beam can be operably connected to the secondbottom beam with a second side telescopic beam stabilizer, and the firstbottom beam can be operably connected to the second bottom beam with abottom telescopic beam stabilizer. The beam stabilizer, or at least aportion thereof, can be fixably attached, or monolithically integral to,one or both beams between which it is operably connected or positionedin either a fixed or translatable configuration in the trial.

Given the teachings provided herein, one of skill will appreciate thateach subhead can be designed/adapted/configured for an operableconnection with interlocking and interconnecting structures that serveto provide alignment and stability between the subhead and a secondsubhead during expansion and/or collapse of the trial. The transverseinterconnection structures are intended to provide stability to the headassembly while at least substantially limiting the movement of the headsto the direction of expansion and/or collapse, such that the relativestability between beams in the trial system during expansion or collapseis improved by at least 10%, 20%, 30%, 40%, 50%, 60%, or 70% over therelative stability between beams in a comparison trial system having thesame structure in the absence of the beam stabilizer configuration. Forexample, both the system and the comparison trial system can each havethe same configuration of 4 subheads that include a first top beam, asecond top beam, a first bottom beam, and a second bottom beam, each ofthe beams having a central axis. The desired, stabilized and/or alignedconfiguration can be, for example, that the central axis of the firsttop beam is at least substantially on (i) a top plane containing thecentral axis of the first top beam and the central axis of a second topbeam and (ii) a first side plane containing the central axis of thefirst top beam and the central axis of a first bottom beam. If thecomparison trial system deviates from the desired stabilized and/oraligned configuration by, for example, 30°, measured as the deviation asthe deflection of a beam's central axis from the desired configuration,then an improvement of at least 10% would represent a deflection of 27°or less, an improvement of at least 20% would represent a deflection of24° or less, an improvement of at least 30% would represent a deflectionof 21° or less, an improvement of at least 40% would represent adeflection of 18° or less, an improvement of at least 50% wouldrepresent a deflection of 15° or less, an improvement of at least 60%would represent a deflection of 12° or less, an improvement of at least70% would represent a deflection of 9° or less, an improvement of atleast 80% would represent a deflection of 6° or less, an improvement ofat least 90% would represent a deflection of 3° or less, an improvementof at least 95% would represent a deflection of 1.5° or less, in someembodiments. One of skill will appreciate that this is merely an exampleof how the % improvement can be calculated. The same, or any similar,approach can be used as a relative measure of improvement due toconfigurations that include one or more beam stabilizers.

In some embodiments, the beam stabilizer can be a telescopingmale/female relationship between two bosses, a male boss configured on afirst beam and a female boss configured on a second beam. In theseembodiments, the male boss is monolithically integral to the first beam,and the female boss is monolithically integral to the second beam, themale boss slidably translating with the female boss to at leastsubstantially confining movement between the first beam and the secondbeam to the transverse movement of expansion and collapse between thebeams.

FIGS. 8A-8D illustrate a staged, bilaterally-expandable trial with beamstabilizers, according to some embodiments. As shown in FIG. 8A, asystem such as system 700 can be used, having the guide tube or barrel815, plunger 860, and retainer 867, the trial 805 being in the expandedstate by turning the knob 840 to obtain the axial proximal-to-distalmovement 879PD of the shim 810 into the trial 805. As shown in FIGS. 8Band 8C, a beam stabilizer 880 can be used to provide a means for anincreased relative stability between beams that frame the top, bottom,first side, and second side of the trial 805. Such means for providingthe increased relative stability between beams can be, for example, atelescopic linear guide configuration having a guide 882 and slider 884.The shim 810 is forced to enter the trial 805 through proximal-to-distalaxial movement 879PD, and the beam stabilizers 880 increase the relativestability of the trial during the distraction procedure.

In some embodiments, the telescopic linear guide comprises a slider anda guide. In some embodiments, the slider can be a plate, and the guidecan be a rail. In some embodiments, the slider can be plate, and theguide can be a member that at least partially circumscribes the plate.In some embodiments, the slider can be a plate, and the guide can be acylinder. It should be appreciated that the guide can be a circularcylinder, an elliptical cylinder, a square cylinder, a rectangularcylinder, a triangular cylinder, a pentagonal cylinder, or hexagonalcylinder. Likewise the slider can be any complementary rigid structure,such as a cylindrical rod, an elliptical rod, a square rod, arectangular rod, a triangular rod, a pentagonal rod, or a hexagonal rod.In some embodiments, the beam stabilizer is an assembly that telescopesto facilitate the expansion and the collapse of the trial. In someembodiments, the slider and the guide translate relative to one anotherto provide the telescopic movement for expansion and collapse of thetrial without a relative rotary motion between the guide and slider.

As shown in FIGS. 8B-8D, the system trial 805 can have abilaterally-expandable system of 4 subheads 816,817,818,819 that includea first top beam 816, a second top beam 817, a first bottom beam 818,and a second bottom beam 819. The mid-region can have 4 flex rods821,822,823,824 that include a first top flex rod 821, a second top flexrod 822, a first bottom flex rod 823, and a second bottom flex rod 824,each of which operably attaches a slider-guide not shown (see, forexample, FIG. 3, 310; and FIG. 7, 701) to it's respective subhead. Asshown in FIG. 8C, each end 806 of the 4 subheads 816,817,818,819 can betapered or otherwise round, configured in the collapsed state in someembodiments, for example, as a bullet-nosed tip to avoid damage to theinner annulus during the distraction procedure.

In some embodiments, a pin can be rigidly connected to each of twosubheads but telescoping within itself, for example, a first portion ofthe pin can be hollow to guide a second portion of the pin to slidablytranslate the second portion as a slider within the guide of the firstportion. In some embodiments, the telescoping arrangement of the beamstabilizers can include a linear connector pin, or other single unitlinear member (cylindrical rod, elliptical rod, triangular rod, squarerod, rectangular rod, trapezoidal rod, pentagonal rod, hexagonal rod,heptagonal rod, octagonal rod, and any other polygonal rod or cylinder)having two ends, each end of which is adapted for operably connecting toa counter-bore hole in one of two subheads between which the pin ispositioned and/or connected.

FIGS. 9A-9D illustrate a staged, bilaterally-expandable trial with beamstabilizers that telescope with one or both subheads having acounter-bore, according to some embodiments. As shown in FIGS. 9A(collapsed configuration) and 9B (expanded configuration), the systemtrial 905 can have a bilaterally-expandable system of 4 subheads916,917,918,919 that include a first top beam 916, a second top beam917, a first bottom beam 918, and a second bottom beam 919. Themid-region can have 4 flex rods 921,922,923,924 that include a first topflex rod 921, a second top flex rod 922, a first bottom flex rod 923,and a second bottom flex rod 924, each of which operably attaches aslider-guide 901 to it's respective subhead. As shown in FIG. 9C(head-only, expanded), each end 906 of the 4 subheads 916,917,918,919can be tapered or otherwise round, configured in the collapsed state insome embodiments, for example, as a bullet-nosed tip to avoid damage tothe inner annulus during the distraction procedure.

As the head expands as shown in FIGS. 9A-9C, the subhead of trial 905can slide on a pin 990 transversely while limited in movement by a means(not visible) of stopping the translational expansion. For example, asshown in FIG. 9D each end of the pin 990 can have a retention head, orpinhead 997 that is retained in the counter-bore 991 of each subhead oftrial 905 by a cap 993 that covers the counter-bore (not visible) toretain the pin 990 upon expansion 905 e and collapse 905 c of the trial905. One of skill will appreciate that in order for the pin 990 totranslate in the subhead of the trial 905 and be retained, (i) the outerdiameter, or transverse dimension, of the pin 990 is less than the innerdiameter, or transverse dimension, of the counter-bore pin guide 995;and (ii) the outer diameter, or transverse dimension, of the pinhead 997is greater than the inner diameter, or transverse dimension, of thecounter-bore pin guide 995. It should also be appreciated that thepinhead 997 can be a cap, a flange, or any other configuration thatresults in the pinhead 997 having a larger diameter or transversedimension than the pin 990 and the inner diameter, or transversedimension, of the counter-bore pin guide 995.

Accordingly, a method of distracting an intervertebral space using thetrials is provided. In some embodiments, the method can comprisecreating a point of entry into an intervertebral disc, theintervertebral disc having a nucleus pulposus surrounded by an annulusfibrosis, and the point of entry having the maximum lateral dimensioncreated through the annulus fibrosis. The methods can include removingthe nucleus pulposus from within the intervertebral disc through thepoint of entry, leaving the intervertebral space for expansion of thehead of the trial within the annulus fibrosis, the intervertebral spacehaving the top vertebral plate and the bottom vertebral plate. Themethods can include inserting the head in the collapsed state throughthe point of entry into the intervertebral space; and, distracting theintervertebral space using a staged, bilateral expansion that includes afirst stage and a second stage. The distracting can include a firststage and a second stage, the first stage including expanding the headlaterally toward the peripheral zones of the top vertebral plate and thebottom vertebral plate; and, the second stage including expanding thehead vertically to distract the intervertebral space, the pressure forthe expansion occurring preferably, and at least primarily, at or nearthe peripheral zones of the top vertebral plate and the bottom vertebralplate. In some embodiments, the lateral dimension of the point of entryranges from about 5 mm to 18 mm, 6 mm to 18 mm, 7 mm to 18 mm, 5 mm to15 mm, 5 mm to 16 mm, 5 mm to 17 mm, or any range therein in incrementsof 1 mm.

In some embodiments, the distracting includes selecting an amount oflateral expansion independent of an amount of vertical expansion. And,in some embodiments, the distracting includes measuring the amount oflateral expansion independent of the amount of vertical expansion.

In some embodiments, the distracting includes as a first stage oflateral expansion, inserting a top wedge into the head between the firsttop beam and the second top beam, the top wedge composing a portion ofthe shim and configured to laterally-expand the first top beam away fromthe second top beam; and, inserting a bottom wedge into the head betweenthe first bottom beam and the second bottom beam, the bottom wedgeconfigured to laterally-expand the first bottom beam away from thesecond bottom beam. And, as a second stage of expansion, inserting afirst side wedge into the head between the first top beam and the firstbottom beam, the first side wedge configured to laterally-expand thefirst top beam away from the first bottom beam; and, inserting a secondside wedge into the head between the second top beam and the secondbottom beam, the second side wedge configured to laterally-expand thesecond top beam away from the second bottom beam.

In some embodiments, the distracting includes selecting a shim having alateral-expansion wedge with angle θ_(L) ranging from 10° to 30° and avertical-expansion wedge with angle θ_(V) ranging from 30° to 50°, theapex of the lateral-expansion wedge and the apex of thevertical-expansion wedge each at least substantially on a single planethat is orthogonal to the central axis of the shim, and the ratio ofθ_(V):θ_(L) ranges from 1:1.25 to 1:4 to stage the bilateral expansionof the head.

In some embodiments, the distracting includes selecting a shim having alateral-expansion wedge with angle θ_(L) ranging from 10° to 90° and avertical-expansion wedge with angle θ_(V) ranging from 10° to 90°, theapex of the lateral-expansion wedge on a first plane and the apex of thevertical expansion wedge on a second plane, both the first plane and thesecond plane being orthogonal to the central axis of the shim andseparated on the central axis at a distance ranging from 2 mm to 10 mmto stage the bilateral expansion of the head.

In some embodiments, the head of the trial can also be used as a “trialshim” for a bilaterally expandable cage by expanding the trialbilaterally and measuring the size of the expanded head to obtain ameasure of the width and the height of the intervertebral space.

One of skill will appreciate that the teachings provided herein aredirected to basic concepts that can extend beyond any particularembodiment, embodiments, figure, or figures. As such, there are severalequivalents that can be contemplated having substantially the samefunction, performed in substantially the same way, for substantially thesame result. As such, it should be appreciated that any examples are forpurposes of illustration and are not to be construed as otherwiselimiting to the teachings. For example, it should be appreciated thatthe devices provided herein can also be used in other areas of the body,and can have slightly varying configurations and adaptations. Thedevices provided herein can be used, for example, in intravertebral bodyprocedures to distract intervertebral bodies in operations that mayinclude the repair of, for example, collapsed, damaged or unstablevertebral bodies suffering from disease or injury.

We claim:
 1. A staged, bilaterally-expandable trial for anintervertebral space, comprising: a bilaterally-expandable shell havinga proximal region with an end, a mid-region, a distal region with anend, and a lumen; the proximal region having a slider-guide; the distalregion having a bilaterally-expandable head with 4 subheads that includea first top beam, a second top beam, a first bottom beam, and a secondbottom beam; and, the mid-region having 4 flex rods that include a firsttop flex rod, a second top flex rod, a first bottom flex rod, and asecond bottom flex rod, each of which operably attaches the slider-guideto it's respective subhead, the shell having a collapsed state and anexpanded state; and, a shim having a proximal region with an end; amid-region; a distal region with an end; a central axis; a top surfacewith a first top-lateral surface and a second top-lateral surface; abottom surface with a first bottom-lateral surface and a secondbottom-lateral surface; a first side surface with a first top-sidesurface and a first bottom-side surface; and, a second side surface witha second top-side surface and a second bottom-side surface; the shimconfigured for a proximal-to-distal axial translation in the lumen ofthe shell that induces a lateral force on the 4 subheads followed by avertical force on the 4 subheads for a staged, bilateral expansion invivo that includes a lateral expansion of the head followed by avertical expansion of the head in an intervertebral space having a topvertebral endplate, a bottom vertebral endplate, and an annulus;wherein, the head has a proximal portion having an end; a distal portionhaving an end; and, a central shell axis of the expanded state; the headconfigured for slidably-engaging with the shim in vivo followingplacement of the trial in the intervertebral space through the annularopening, the slidably-engaging including axially-translating the shim inthe lumen of the shell from the proximal end of the lumen toward thedistal end of the lumen in vivo; the translating including keeping thecentral shim axis at least substantially coincident with the centralshell axis during the translating.
 2. The trial of claim 1, wherein thehead has a transverse cross-section in the collapsed state having amaximum dimension ranging from 5 mm to 18 mm for placing the frame in anintervertebral space through an annular opening for expansion in theintervertebral space; and, a transverse cross-section in the expandedstate having a maximum dimension ranging from 6.5 to 28 mm in theintervertebral space; and, the shim has a transverse cross-section witha maximum dimension ranging from 5 mm to 18 mm for translating the shimin the lumen of the shell.
 3. The trial of claim 1, wherein the shim hasa horizontal wedge configured to laterally-expand the trial, and avertical wedge configured to vertically-expand the trial.
 4. The trialof claim 1, wherein the shim has a top wedge configured tolaterally-expand the first top beam away from the second top beam, abottom wedge configured to laterally-expand the first bottom beam awayfrom the second bottom beam, a first side wedge configured tovertically-expand the first top beam away from the first bottom beam,and a second side wedge configured to vertically-expand the second topbeam away from the second bottom beam; the proximal portion of the firsttop beam and the proximal portion of the second top beam are configuredto complement the top wedge at the onset of the lateral expansion duringthe proximal-to-distal axial translation; the proximal portion of thefirst bottom beam and the proximal portion of the second bottom beam areconfigured to complement the bottom wedge at the onset of the lateralexpansion during the proximal-to-distal axial translation; and, thedistance, D_(STAGING), between the onset of the lateral expansion andthe onset of the vertical translation ranges from 2 mm to 10 mm.
 5. Thetrial of claim 4, wherein the proximal portion of the first top beam andthe proximal portion of the first bottom beam are configured tocomplement the first side wedge during the proximal-to-distal axialtranslation for the vertical expansion; and, the proximal portion of thesecond top beam and the proximal portion of the second bottom beam areconfigured to complement the second side wedge during theproximal-to-distal axial translation for the vertical expansion.
 6. Thetrial of claim 1, wherein, the first top beam includes a proximalportion having an end, a distal portion having an end, and a centralaxis; the first top beam configured for contacting a first top chamferof the shim in the expanded state, the central axis of the first topbeam at least substantially on (i) a top plane containing the centralaxis of the first top beam and the central axis of a second top beam and(ii) a first side plane containing the central axis of the first topbeam and the central axis of a first bottom beam; the second top beamincludes a proximal portion having an end, a distal portion having anend, and a central axis; the second top beam configured for contacting asecond top chamfer of the shim in the expanded state, the central axisof the second top beam at least substantially on (i) the top plane and(ii) a second side plane containing the central axis of the second topbeam and the central axis of a second bottom beam; the first bottom beamincludes a proximal portion having an end, a distal portion having anend, and a central axis; the first bottom beam configured for contactinga first bottom chamfer of the shim in the expanded state, the centralaxis of the first bottom beam at least substantially on (i) a bottomplane containing the central axis of the first bottom beam and thecentral axis of a second top beam and (ii) the first side plane; and,the second bottom beam includes a proximal portion having an end, adistal portion having an end, and a central axis; the second bottom beamconfigured for contacting a second bottom chamfer of the shim in theexpanded state, the central axis of the second bottom beam being atleast substantially on (i) the bottom plane and (ii) a second side planecontaining the central axis of the second bottom beam and the second topbeam.
 7. The trial of claim 1, wherein, the first top beam includes aproximal portion having an end, a distal portion having an end, and acentral axis; the first top beam configured for contacting a firsttop-lateral surface of the shim and a first top-side surface of the shimin the expanded state, the central axis of the first top beam at leastsubstantially on (i) a top plane containing the central axis of thefirst top beam and the central axis of a second top beam and (ii) afirst side plane containing the central axis of the first top beam andthe central axis of a first bottom beam; the second top beam includes aproximal portion having an end, a distal portion having an end, and acentral axis; the second top beam configured for contacting the secondtop-lateral surface of the shim and the second top-side surface of theshim in the expanded state, the central axis of the second top beam atleast substantially on (i) the top plane and (ii) a second side planecontaining the central axis of the second top beam and the central axisof a second bottom beam; the first bottom beam includes a proximalportion having an end, a distal portion having an end, and a centralaxis; the first bottom beam configured for contacting the firstbottom-lateral surface of the shim and the first bottom-side surface ofthe shim in the expanded state, the central axis of the first bottombeam at least substantially on (i) a bottom plane containing the centralaxis of the first bottom beam and the central axis of a second top beamand (ii) the first side plane; and, the second bottom beam includes aproximal portion having an end, a distal portion having an end, and acentral axis; the second bottom beam configured for contacting thesecond bottom-lateral surface of the shim and the second bottom-sidesurface of the shim in the expanded state, the central axis of thesecond bottom beam being at least substantially on (i) the bottom planeand (ii) a second side plane containing the central axis of the secondbottom beam and the second top beam.
 8. The trial of claim 1, whereinthe shim comprises a lateral-expansion wedge with angle θ_(L) rangingfrom 10° to 30° and a vertical-expansion wedge with angle θ_(V) rangingfrom 30° to 50°, the apex of the lateral-expansion wedge and the apex ofthe vertical-expansion wedge each at least substantially on a singleplane that is orthogonal to the central axis of the shim, and the ratioof θ_(V):θ_(L) ranges from 1:1.25 to 1:4 to stage the bilateralexpansion of the head.
 9. The trial of claim 1, wherein the wherein theshim comprises a lateral-expansion wedge with angle θ_(L) ranging from10° to 90° and a vertical-expansion wedge with angle θ_(V) ranging from10° to 90°, the apex of the lateral-expansion wedge on a first plane andthe apex of the vertical expansion wedge on a second plane, both thefirst plane and the second plane being orthogonal to the central axis ofthe shim and separated on the central axis at a distance ranging from 2mm to 10 mm to stage the bilateral expansion of the head.
 10. The trialof claim 1, wherein the shell is a single-unit formed from a single bodyof material, and the slider-guide, head, and flex rods aremonolithically integral.
 11. The trial of claim 1, wherein the proximalend of the shim is configured to receive an axial proximal-to-distalforce through an actuation bar for the axial translation, the actuationbar having a proximal portion with a proximal end, a distal portion witha distal end, and configured to transfer the axial proximal-to-distalforce to the shim through the slider-guide.
 12. The trial of claim 1,wherein the first top beam is operably connected to the second top beamwith a top telescopic beam stabilizer, the first top beam is operablyconnected to the first bottom beam with a first side telescopic beamstabilizer, the second top beam is operably connected to the secondbottom beam with a second side telescopic beam stabilizer, the firstbottom beam is operably connected to the second bottom beam with abottom telescopic beam stabilizer.
 13. A system for distracting anintervertebral space, the system comprising a bilaterally-expandableshell having a proximal region with an end, a mid-region, a distalregion with an end, and a lumen; the proximal region having aslider-guide; the distal region having a bilaterally-expandable headwith 4 subheads that include a first top beam, a second top beam, afirst bottom beam, and a second bottom beam; and, the mid-region having4 flex rods that include a first top flex rod, a second top flex rod, afirst bottom flex rod, and a second bottom flex rod, each of whichoperably attaches the slider-guide to it's respective subhead, the shellhaving a collapsed state and an expanded state; a shim having a proximalregion with an end; a mid-region; a distal region with an end; a centralaxis; a top surface with a first top-lateral surface and a secondtop-lateral surface; a bottom surface with a first bottom-lateralsurface and a second bottom-lateral surface; a first side surface with afirst top-side surface and a first bottom-side surface; and, a secondside surface with a second top-side surface and a second bottom-sidesurface; the shim configured for a proximal-to-distal axial translationin the lumen of the shell that induces a lateral force on the 4 subheadsfollowed by a vertical force on the 4 subheads for a staged, bilateralexpansion in vivo that includes a lateral expansion of the head followedby a vertical expansion of the head in an intervertebral space having atop vertebral endplate, a bottom vertebral endplate, and an annulus; anactuation bar, the actuation bar having a proximal portion with aproximal end, a distal portion with a distal end, and configured totransfer the axial proximal-to-distal force to the shim through theslider-guide; the shim configured to receive an axial proximal-to-distalforce through the actuation bar for the axial translation; and, anactuation means operably attached to the proximal end of the actuationbar to transfer the axial proximal-to-distal force to the shim throughthe distal end of the actuation bar; wherein, the head has a proximalportion having an end; a distal portion having an end; and, a centralshell axis of the expanded state; the head configured forslidably-engaging with the shim in vivo following placement of the trialin the intervertebral space through the annular opening, theslidably-engaging including axially-translating the shim in the lumen ofthe shell from the proximal end of the lumen toward the distal end ofthe lumen in vivo; the translating including keeping the central shimaxis at least substantially coincident with the central shell axisduring the translating.
 14. The system of claim 13 further comprising aretractable retention plunger configured for retaining the trial in thecollapsed state and releasing the trial for expansion into the expandedstate.
 15. The system of claim 13, wherein the first top beam isoperably connected to the second top beam with a top telescopic beamstabilizer; wherein, the first top beam is operably connected to thefirst bottom beam with a first side telescopic beam stabilizer, thesecond top beam is operably connected to the second bottom beam with asecond side telescopic beam stabilizer, the first bottom beam isoperably connected to the second bottom beam with a bottom telescopicbeam stabilizer.
 16. The system of claim 13, wherein the actuation barreceives the axial proximal-to-distal force from an actuation screw thatis operably attached to the proximal end of the actuation bar andtransfers the force to the shim through the distal end of the actuationbar.
 17. The system of claim 13, wherein the head has a transversecross-section in the collapsed state having a maximum dimension rangingfrom 5 mm to 18 mm for placing the frame in an intervertebral spacethrough an annular opening for expansion in the intervertebral space;and, a transverse cross-section in the expanded state having a maximumdimension ranging from 6.5 to 28 mm in the intervertebral space; and,the shim has a transverse cross-section with a maximum dimension rangingfrom 5 mm to 18 mm for translating the shim in the lumen of the shell.18. The system of claim 13, wherein the shim has a horizontal wedgeconfigured to laterally-expand the trial, and a vertical wedgeconfigured to vertically-expand the trial.
 19. The system of claim 13,wherein the shim has a top wedge configured to laterally-expand thefirst top beam away from the second top beam, a bottom wedge configuredto laterally-expand the first bottom beam away from the second bottombeam, a first side wedge configured to vertically-expand the first topbeam away from the first bottom beam, and a second side wedge configuredto vertically-expand the second top beam away from the second bottombeam; the proximal portion of the first top beam and the proximalportion of the second top beam are configured to complement the topwedge at the onset of the lateral expansion during theproximal-to-distal axial translation; the proximal portion of the firstbottom beam and the proximal portion of the second bottom beam areconfigured to complement the bottom wedge at the onset of the lateralexpansion during the proximal-to-distal axial translation; and, thedistance, D_(STAGING), between the onset of the lateral expansion andthe onset of the vertical translation ranges from 2 mm to 10 mm.
 20. Thesystem of claim 19, wherein the proximal portion of the first top beamand the proximal portion of the first bottom beam are configured tocomplement the first side wedge during the proximal-to-distal axialtranslation for the vertical expansion; and, the proximal portion of thesecond top beam and the proximal portion of the second bottom beam areconfigured to complement the second side wedge during theproximal-to-distal axial translation for the vertical expansion.
 21. Thesystem of claim 13, wherein, the first top beam includes a proximalportion having an end, a distal portion having an end, and a centralaxis; the first top beam configured for contacting a first top chamferof the shim in the expanded state, the central axis of the first topbeam at least substantially on (i) a top plane containing the centralaxis of the first top beam and the central axis of a second top beam and(ii) a first side plane containing the central axis of the first topbeam and the central axis of a first bottom beam; the second top beamincludes a proximal portion having an end, a distal portion having anend, and a central axis; the second top beam configured for contacting asecond top chamfer of the shim in the expanded state, the central axisof the second top beam at least substantially on (i) the top plane and(ii) a second side plane containing the central axis of the second topbeam and the central axis of a second bottom beam; the first bottom beamincludes a proximal portion having an end, a distal portion having anend, and a central axis; the first bottom beam configured for contactinga first bottom chamfer of the shim in the expanded state, the centralaxis of the first bottom beam at least substantially on (i) a bottomplane containing the central axis of the first bottom beam and thecentral axis of a second top beam and (ii) the first side plane; and,the second bottom beam includes a proximal portion having an end, adistal portion having an end, and a central axis; the second bottom beamconfigured for contacting a second bottom chamfer of the shim in theexpanded state, the central axis of the second bottom beam being atleast substantially on (i) the bottom plane and (ii) a second side planecontaining the central axis of the second bottom beam and the second topbeam.
 22. The system of claim 13, wherein, the first top beam includes aproximal portion having an end, a distal portion having an end, and acentral axis; the first top beam configured for contacting a firsttop-lateral surface of the shim and a first top-side surface of the shimin the expanded state, the central axis of the first top beam at leastsubstantially on (i) a top plane containing the central axis of thefirst top beam and the central axis of a second top beam and (ii) afirst side plane containing the central axis of the first top beam andthe central axis of a first bottom beam; the second top beam includes aproximal portion having an end, a distal portion having an end, and acentral axis; the second top beam configured for contacting the secondtop-lateral surface of the shim and the second top-side surface of theshim in the expanded state, the central axis of the second top beam atleast substantially on (i) the top plane and (ii) a second side planecontaining the central axis of the second top beam and the central axisof a second bottom beam; the first bottom beam includes a proximalportion having an end, a distal portion having an end, and a centralaxis; the first bottom beam configured for contacting the firstbottom-lateral surface of the shim and the first bottom-side surface ofthe shim in the expanded state, the central axis of the first bottombeam at least substantially on (i) a bottom plane containing the centralaxis of the first bottom beam and the central axis of a second top beamand (ii) the first side plane; and, the second bottom beam includes aproximal portion having an end, a distal portion having an end, and acentral axis; the second bottom beam configured for contacting thesecond bottom-lateral surface of the shim and the second bottom-sidesurface of the shim in the expanded state, the central axis of thesecond bottom beam being at least substantially on (i) the bottom planeand (ii) a second side plane containing the central axis of the secondbottom beam and the second top beam.
 23. The system of claim 13, whereinthe shim comprises a lateral-expansion wedge with angle θ_(L) rangingfrom 10° to 30° and a vertical-expansion wedge with angle θ_(V) rangingfrom 30° to 50°, the apex of the lateral-expansion wedge and the apex ofthe vertical-expansion wedge each at least substantially on a singleplane that is orthogonal to the central axis of the shim, and the ratioof θ_(V):θ_(L) ranges from 1:1.25 to 1:4 to stage the bilateralexpansion of the head.
 24. The system of claim 13, wherein the shimcomprises a lateral-expansion wedge with angle θ_(L) ranging from 10° to90° and a vertical-expansion wedge with angle θ_(V) ranging from 10° to90°, the apex of the lateral-expansion wedge on a first plane and theapex of the vertical expansion wedge on a second plane, both the firstplane and the second plane being orthogonal to the central axis of theshim and separated on the central axis at a distance ranging from 2 mmto 10 mm to stage the bilateral expansion of the head.
 25. The system ofclaim 13, wherein the shell is a single-unit formed from a single bodyof material, and the slider-guide, head, and flex rods aremonolithically integral.
 26. A method of distracting an intervertebralspace using the trial of claim 1, the method comprising: creating apoint of entry into an intervertebral disc, the intervertebral dischaving a nucleus pulposus surrounded by an annulus fibrosis, and thepoint of entry having the maximum lateral dimension created through theannulus fibrosis; removing the nucleus pulposus from within theintervertebral disc through the point of entry, leaving theintervertebral space for expansion of the head of the trial of claim 1within the annulus fibrosis, the intervertebral space having the topvertebral plate and the bottom vertebral plate; inserting the head inthe collapsed state through the point of entry into the intervertebralspace; and, distracting the intervertebral space using a staged,bilateral expansion that includes a first stage and a second stage, thefirst stage including expanding the head laterally toward the peripheralzones of the top vertebral plate and the bottom vertebral plate; and,the second stage including expanding the head vertically to distract theintervertebral space.
 27. The method of claim 26 further comprisingretaining the trial with a retractable retention plunger and retractingthe plunger to expand the trial.
 28. The method of claim 26, wherein thelateral dimension of the point of entry ranges from about 5 mm to about18 mm.
 29. The method of claim 26, wherein the distracting includesselecting an amount of lateral expansion independent of an amount ofvertical expansion.
 30. The method of claim 26, wherein the distractingincludes measuring the amount of lateral expansion independent of theamount of vertical expansion.